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Background: Know: NOC Recognize: IPv4, 802.1q, Controlled load, best effort Priorities Network Traffic Priorities: Once the network can distinguish phone calls and internet browsing,priority processing can ensure that simultaneously downloading on Internet and making phone call will not be interrupted.In order to ensure the accuracy of the priority processing, all traffic must be identified within the network backbone.Priority processing of data at the workstation terminal may be problems due to attacks or malicious destruction. Hackers can intentionally mark ordinary data as high priority to steal bandwidth of important commercial applications,resulting in failure of the applications. This situation is called a denial of service attack.By analyzing all traffic when entering network, service can detect security attacks and stop it before any harm being caused. LAN switches allows packet prioritization exist.Higher priority services can not be impacted by lower priority services via switches to reduce delay. In order to provide priority levels,each port of switch must have at least two queues.Although at each port,more queue can provide more fine-priority option, in a LAN,each port requires four or more queues is unlikely.So switches to determine next step of service queue through its queuing mechanism can use the following two kinds of queuing up. Strict Priority Queuing(SPQ)is one of the most simple queuing up.SPQ firstly server the highest priority queue until the queue is empty, and then server the next high priority queue, and so on. The advantage of this method is the high priority traffic is always processed before low-priority traffic.However,the low-priority traffic is likely to be completely blocked by high-priority traffic. Weighted Round Robin(WRR)is the queuing up can provide service for all queues,and assigning priority to higher priority queue.In most cases, compared to a relatively low priority queue ,WRR will firstly deal with the higher one.But when the service receive a lot of higher priority ,WRR will not completely block the lower priority businesses. Qos can be judged by the packet’s 802.1Q priority.The tag defines the following eight "user priority" levels that provide signals to network devices as to the class of service that the frame should receive: Priority 7 Network control traffic such as router configuration messages Priority 6 Voice traffic, such as NetMeeting, that is especially sensitive to jitter Priority 5 Video, which is high bandwidth and sensitive to jitter Priority 4 Controlled load, latency-sensitive traffic such as SNA transactions Priority 3 Better than best effort, which would include important business traffic that can tolerate some delay Priority 2 Best-effort traffic Priority 1 The default mode if none is specifiedPriority 0 Noncritical traffic such as backups, noncritical replications, some electronic mail, and so on For IPv4 Type of Service: ToS is defined as a six bit differentiated service code point. IPv4 ToS is mainly to specify the sending host’s path through internet and design the method of datagram be handled For example, in this case one TOS(Type of Service) field value would prefer a low delay while the other would prefer a high reliably one. Totally 8 bits were allocated to a TOS field in IP Header. The precedence bits are from 0 to 7 and the default is 000 which means higher is better, explained in the following table: Precedence Decimal of 6 left Bits Description 111 56 Network Control 110 48 Internetwork Control 101 40 CRITIC/ECP 100 32 Flash Override 011 24 Flash 010 16 Immediate 001 8 Priority 000 0 Routine References 1.http://en.wikipedia.org/wiki/Quality_of_service 2.http://www.linktionary.com/q/qos.html Category:All